Filtering units consisting of centrally apertured plates or discs of fibrous substances are known from U.S. Pat. No. 2,435,115 to Alsop. The units are stacked coaxially and connected together.
In U.S. Pat. No. 4,347,208 to Southall, a method is disclosed for making a filter cell having two cellulosic fiber containing filter media with a sealed periphery. The peripheries of the filter media are compressed to form a flange. The filter media is then placed in a mold which surrounds the flanges. A thermoplastic polymer is then injected into the mold to form a seal around the flanges.
Additional examples of filter cells are disclosed in U.S. Pat. No. 2,788,901 to Boeddinghaus et al, U.S. Pat. No. 3,082,587 to Brimberg and U.S. Pat. No. 4,783,262 to Ostreicher et al.